8x8 post fixed base 5

[JoeBaseplate]

I can't recall to have ever fixed the base of wood post. I have a situation where I might have to do that. I couldn't find an appropriate simpson base anchor for that. Is a custom built base plate the way to go? I am thinking of a steel base plate with welded HSS to fit the 8x8 in.

 

[racookpe1978]

Are you trying to prevent termite/rot damage to the post by elevating it?

Or trying to minimize the sideways movement of the bottom of the post by anchoring the steel widget down to the underlaying concrete (with a vertical through-bolt perhaps); so that you want the steel widget to be able to be bolted firmly to the wood post? (That is, through bolt holds the steel to the concrete by resisting shear, and the secondary bolts hold the steel to the wood by resisting pull-out?

 

[MiketheEngineer]

If you are looking for a moment transfer bracket - they don't exist.

A company call Sturdi-bracket makes something they say will transfer "some" moment. Google that. Be careful - it is capable in one direction only.

An HSS bracket might work - sort of. If there is any "wiggle" in the timber to HSS - then you will lose some capacity.

 

[boo1]

Consider Simpson ABU88 and ABU88R

http://www.strongtie.com/products/connectors/AB-ABA-ABE-ABU.asp

These post bases feature 1" standoff height above concrete floors, code-required when supporting permanent structures that are exposed to the weather or water splash, or in basements. They reduce the potential for decay at post and column ends.

 

[JedClampett]

If this is for appearance only (you need it to look like wood), why don't you use a 5 inch square steel HSS and add wood facing?

 

[JoeBaseplate]

Actually after getting some more info, re-configuring a few things here and there, I don't need a fixed base for moment transfer....I know that would be a pain.

But I do need a base that works in uplift as well as shear in both directions. I should be able to find that in Simposn for 8x8, I think.

 

[JoeBaseplate]

Its good to know though that you can't really fix the base of a wood post and the idea of using steel and cladding it with wood is a good one for future reference.

 

[MiketheEngineer]

IF you can bury the post - say 4'-5' down you will be able to generate a moment connection. But for how many years?? Treated wood says 20???

And being in that industry - seems to work....

 

[JoeBaseplate]

Mike, this is the first time I heard about studi-bracket, thanks for that. If I ever need to fix the base, thats what I am using.

 

[msquared48]

CB88 would work for your needs just fine.

Mike McCann
MMC Engineering

 

[racookpe1978]

8x8 wood post is (nowdays) 7.5 x 7.5 inches.

So, you'd need a short section of HSS with an inside dimension of 7.5 x 7.5 inches, then weld that to a backing plate (of 1/4 or 3/8 plate ?) 8.5 x 8.5 with a cheap, easy fillet fillet.

To resist pullout, use 2x 1/2 bolts through the HSS.

Alt: Bend a 1/4 or 5/16 thick plate 8 inches wide into a U with inside width of 7.5 inches. Use 1, 2, or 4 anchor bolts into the slab/foundation on the bottom of the "U", and clamp the two walls of the "U" into the wood post with through bolts.

 

[hokie66]

The trouble with any device to create a moment connection of a timber post is that wood shrinks across the grain, and depending on the species, the shrinkage can be quite a lot. Unless you are going to tighten the bolts periodically, it is not a good idea.

 

[Teguci]

Maybe something like this would provide moment resistance and allow for the shrinkage hokie mentioned?

 

[hawkaz]

I have designed brackets similar to the sturdi-bracket before, but only for very lightly loaded structures such as trellises.

Hokie's comment regarding shrinkage is valid. A bigger problem is the installation. We need the bolts to be snug to the wood in order to resist the moment. The bolt holes will almost always be overdrilled- killing the fixity.

 

[woodman88]

I have used base plates and 1/2" knife plates with thru bolts for small shade trellises.
For higher load conditions, I would use two vertical plates welded together and to a base plate. Designed for the moment required. Bolt the post to the each plate with plate washers. Design the wood connection on perpendicular compression of wood against the plate washer to resist the moment in each direction. Using the bolts only in tension.
This would of course be too visual for most architects or owners.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[hokie66]

Teguci's effort deserves a tick.

 

[JoeBaseplate]

Teguci, wow thanks for the detail. That would certainly do it.

 

[rowingengineer]

Why not scope the timber over a bit of steel SHS, then bolt the two together.

How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

 

[hokie66]

RE,
Cross grain shrinkage. Teguci's solution goes a long way toward dealing with the loosening of the connection due to shrinkage of the timber.

 

[dik]

using pressure treated lumber and glulam rivets in lieu of screws...
nice detail. The spacer at the bottom elevates the wood and avoids the rounded fillet...

Dik